The brass cartridge cases of rifle ammunition are reusable and many shooters reload their cases by resizing, repriming, and recharging the cartridges with powder, and reseating a new projectile. Reloading can be economic because it can provide a shooter with more ammunition and higher quality ammunition for a given budget. Reloading also allows shooters to customise the ammunition to their individual requirements, for example to suit their needs of accuracy, bullet-type or velocity.
The brass case may often be the most expensive component of a cartridge and therefore it is advantageous to re-use it as many times as possible. The process of resizing and reseating bullets in the case work hardens the neck of the case, which can result in an increase in neck tension and therefore increased chamber pressure. Work hardening can also cause the neck to become brittle or to crack as the brass loses its malleability. A work hardened case may be unable to survive swaging back into shape during the process of resizing.
The effects of work hardening can be alleviated by annealing, which makes brass softer and less brittle. Annealing involves heating a substance to a specified temperature for a specified length of time and then allowing the substance to cool. There are complexities in annealing a cartridge case because the heating must be localised at the neck of the case. The head of the case must avoid being annealed and remain hard because if it is overly softened the case will be unsafe to use.
Conventional ways of annealing cartridge cases include applying heat to the neck using gas burners or a molten alloy of lead. The temperature in the rest of the case may be controlled by standing the case in water. However these techniques have inherent repeatability and safety issues. Heating the neck with a torch makes it difficult to evenly heat all of the neck. These techniques are also not easily repeatable from case to case but repeatability is required for consistent results.
Induction annealing is the process of annealing by the application of heat to metal by electromagnetic induction. Currents are induced in the metal, which is resistively heated. Induction annealing is used at the industrial level of case manufacturing but it has not been available as a practical option for the domestic reloader because of the complexities in tailoring induction annealing equipment to the requirements of individual cartridge cases.
It is an object of the invention to provide an apparatus for induction annealing a neck of a cartridge case. There is a need for an induction annealing apparatus suitable for non-industrial purposes, for example, use domestically.
Alternatively, it is an object of the invention to at least provide the public with a useful choice.